Field: This invention relates to snowmobile skis, and more particularly to steering skis or snowmobiles and similar vehicles.
State of the Art: Steering a snowmobile is typically accomplished by a pair of steering, skis pivotally attached to the front of the snowmobile. The steering skis glide over the surface of the snow and may be angularly turned from side-to-side in response to movement of a pair of handlebars grasped by a user. The snowmobile generally follows in the direction the skis are pointed.
Under most snow conditions, especially at high speeds, steering skis, when turned, have a tendency to slide sideways, i.e., xe2x80x9cplowxe2x80x9d forward over the surface of the snow rather than tracking as intended. The turning radius of the snowmobile thus becomes larger than anticipated, and may result in the user hitting something or losing control of the vehicle. If the sliding ski happens to suddenly xe2x80x9ccatchxe2x80x9d in the snow, the momentum of the snowmobile can cause it to overturn and injure the rider. This situation is particularly hazardous under snowmobile racing circumstances where the snowmobiles are driven at high speed. If a racer does not make a turn as anticipated, or suddenly loses control of his snowmobile, he can cause a high-speed accident, resulting in injury to the racers.
Various methods have been employed to lend increased predictability and control to snowmobile steering skis. One of the more common methods is inclusion of a longitudinal keel along the underside or running surface of the ski. The keel bites into the surface of the snow and enhances steering characteristics, particularly at high speeds.
U.S. Design Patent Des. 366,014 to Lindquist et al. dated Jan. 9, 1996 illustrates a conventional snowmobile ski having a straight central keel. The top surface of the ski has a continuous head along each edge and a plurality of very small, (thin in width and short in depth) straight, longitudinal ribs along the running (bottom) surface of the ski. The nature of a design patent is to illustrate aesthetic (non-functional) features. Thus, the upper beads and lower ribs appear to be non-functional in nature. Further, this design patent was filed about two years after Priority application Ser. No. 08/106,344 filed Aug. 12, 1993, identified herein above as a parent application to the instant application. That parent application illustrates and describes snowmobile skis having functional, multiple curved keels. The cited design patent shows, functionally, only a straight center keel of conventional shape and purpose.
A keel for a snowmobile steering ski is disclosed in U.S. Pat. No. 3,632,126 to Shorrock. The keel disclosed in Shorrock has a straight running edge, and is adjustable to compensate for wear. U.S. Pat. No. 3,711,109 to Hofbauer discloses a snowmobile steering ski having a very short, curved keel resiliently attached to the ski runner. U.S. Pat. No. 3,643,978 to Westberg discloses a short curved flange which may be attached to the edge of a snowmobile ski, and which is intended to function similar to a keel.
U.S. Pat. No. 5,040,818 and 5,145,201 to Metheny illustrate snowmobile skies having a central keel with a planar lower-surface as a part of a ski which has a laterally arched lower running surface.
Although the above inventions represent alternatives to a snowmobile ski without a keel, they are subject to several problems. The weight of both the snowmobile and the user is distributed evenly over the flat running surface of the skis in Shorrock, which places a portion of the weight at the ends of the straight keel. This makes the skis difficult to turn and lessens its usefulness. The bite of the keel into the surface of the snow is also distributed over a large area instead of concentrated in the most efficient location directly beneath the steering spindles. The short keel in Hofbauer tends to provide a concentration of weight beneath the steering spindles, but the amount of bite is reduced in soft snow due its short length. Also, because it is hinged, it tends to retract on hard snow pack or on ice, when a keel is very important. The short flange in Westberg also tends to concentrate weight beneath the steering spindles, but since it mounts on the edge of the ski, it actually exacerbates the problem of the ski xe2x80x9ccatchingxe2x80x9d in the snow during a turn, causing a loss of control even at moderate speeds. (The phenomenon is similar to the effect of a downhill skier catching a downhill edge during a turn.) Also, such short keels do not provide steering stability during straight runs and show a reduced steering ability in soft snow.
The inventions disclosed in Shorrock, Hofbauer and Westberg bring to light what has heretofore been a dilemma with respect to the design of snowmobile steering skis. Increased positive steering brought about by a long keel comes at the expense of ease of steering. Accordingly, a short keel makes the skis easier to steer, but reduces the amount of positive control. There is a need for a snowmobile steering ski that provides improved controllability and positive turning without a concomitant increase in steering difficulty.
The snowmobile steering ski of the present application includes an elongated ski having at least a pair of protruding keels that emerge from the bottom running surface of the ski runner proximal the front end of the ski. At least one keel gradually increases in its depth of protrusion with respect to the bottom running surface of the ski to a maximum protrusion at a point on the ski bottom which is preferably close to the ski connector for connection to the steering spindles of the snowmobile. The keel may then gradually decrease in its protrusion depth to merge substantially back into the bottom running surface proximal the rear end of the ski.
Several significant advantages result from the design of the improved snowmobile steering ski. Positive steering is improved because the keel may be made to extend along substantially the entire length of the bottom running surface of the ski. Further, the maximum bite of the keel into the snow is in the most efficient position substantially directly beneath the steering spindles. The ski is easy to turn, however, because the keel design results in a lesser percentage of snowmobile and user weight being distributed at the ends of the keel.
In a preferred embodiment, both the ski and its protruding keels are curved through their mid-sections, with curves being slightly upward away from the snow surface and with the curvature of the keel having a similar or slightly smaller radius of curvature than that of the ski. A smaller radius of curvature of one or more of the keels causes the ends of the keel to merge substantially into the curved bottom running surface of the ski. However, a ski and keel curved to substantially the same radius of curvature also works well for the purposes of the invention.
In another embodiment, the ski is curved slightly upward through its mid section and the keel tapers in either direction from a point of maximum protrusion below the steering spindles attachment region of the ski into the bottom surface of the ski. In still another embodiment, the running surface of the ski is flat, i.e. a straight, substantially planar surface, and the keel is curved in a convex shape. In yet another embodiment, the ski runner is flat, i.e. substantially straight in a longitudinal direction, and the keel tapers substantially linearly in either direction from a point of maximum depth below the steering spindles to merge substantially with the bottom surface of the ski near the front and rear of the running surface of the ski.
Several additional advantages result from a steering ski having a slightly curved bottom running surface. The curved ski runner carries the largest percentage of snowmobile and user weight substantially directly under the steering spindles of the snowmobile rather than evenly distributed over the bottom surface of the ski. This produces more positive turning and permits the snowmobile to maneuver faster through a turn without losing steering stability during straight-away runs; The ends of the keel also carry a lesser percentage of weight which makes the ski easier to steer. Keel length, however, may remain long to provide increased positive steering and good tracking during straight runs. Keel penetration into the snow is thus concentrated where it is most effective, and reduced near the ends of the ski to provide easier steering. These advantages exist for a curved ski even if the ski has no keel, although typically a keelless curved ski would be fitted with a wear bar which substantially conformed to the curved running surface of the ski.